Major different. The P67 is the same height as the Grand, minus the raised square part on the Grand. So, it's a bit shorter. It's the same thickness, front to back. Slightly wider, by about 4mm, but the P67 feels smaller in hand, because of the rounded corners. The switch mechanism is completely different. The P67 is a side button. The lock mechanism is internal. Instead of twisting the button, as on the Grand, there is an internal plastic piece that you slide to the right, which separates the top of the battery from the contact. Also, there is no drip well on the P67. It's flat around the 510 connector.